Structural Engineering Award of Excellence: Lakhta Center, St. Petersburg

Ahmad Abdelrazaq
Senior Executive Vice President
Samsung C&T Corporation, Chicago

Five Twisting Tower Forms Become One

In spite of its complex geometry, the Lakhta Center’s steel structure is woven seamlessly within its architectural fabric. The project is composed of five individual tower forms that twist and taper as they rise, thus resulting in a tower that rotates 90 degrees from the base to the tip of the spire. The structure utilizes all vertical elements to resist wind and seismic lateral loads and maximize overall building stiffness. Significant wind-tunnel studies were performed, establishing that the variations in the building’s shape and its vented spire would facilitate a favorable wind response.

As the tower rises, significant changes in the floor plate shape and area required innovative structural engineering solutions. The lateral load-resisting system of the tower consists of a 26-meter diameter reinforced concrete central core wall that is linked with 10 exterior composite steel reinforced and concrete columns, through 10 two-story equally-spaced composite outriggers. These outriggers, consisting of a structural steel truss encased in concrete, transfer the outrigger chord forces to the core wall though an external diaphragm ring slab. A new composite-steel floor framing system was adopted for long spans and changes in the building’s geometry. The effects of biaxial load transfer from the exterior columns is minimized due to their taper and twist. The multi-story stiffened box foundation evenly distributes tower loads to the foundation piles, instead of a very thick pile-supported raft. Due to reduction in steel weight, pre-assembly fabrication of larger sections was possible, as well as a significant reduction in piling and foundation materials.

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